Primes expressible as concatenation of phi(sigma(n)) and sigma(phi(n)).

Terms

a(0) =11a(1) =23a(2) =43a(3) =67a(4) =127a(5) =631a(6) =839a(7) =3631a(8) =1831a(9) =4831a(10) =3691a(11) =6491a(12) =108127a(13) =80363a(14) =108127a(15) =336403a(16) =132961a(17) =288403a(18) =144961a(19) =504403a(20) =384403a(21) =192961a(22) =384403a(23) =384403a(24) =384403a(25) =432511a(26) =864511a(27) =384961a(28) =432961a(29) =640847